U.S. patent number 8,094,749 [Application Number 12/559,824] was granted by the patent office on 2012-01-10 for signaling format for wireless communications.
This patent grant is currently assigned to Broadcom Corporation. Invention is credited to Amit G. Bagchi, Christopher J. Hansen, George Kondylis, Jason Alexander Trachewsky.
United States Patent |
8,094,749 |
Hansen , et al. |
January 10, 2012 |
Signaling format for wireless communications
Abstract
Methods, devices and systems for wireless communication generate
signals by determining whether legacy devices are within a proximal
region of the wireless communication. When at least one legacy
device is within the proximal region, a frame is formatted to
include a preamble field, a signal field, and a data field.
Further, the uncoded bits are encoded according to a coding format.
The coding format is determined according to bits in the preamble
and applicable sub-field lengths.
Inventors: |
Hansen; Christopher J.
(Sunnyvale, CA), Trachewsky; Jason Alexander (Menlo Park,
CA), Bagchi; Amit G. (Mountain View, CA), Kondylis;
George (Palo Alto, CA) |
Assignee: |
Broadcom Corporation (Irvine,
CA)
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Family
ID: |
34841893 |
Appl.
No.: |
12/559,824 |
Filed: |
September 15, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100002672 A1 |
Jan 7, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11056155 |
Feb 14, 2005 |
7590189 |
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10778754 |
Jan 9, 2007 |
7162204 |
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10778751 |
Sep 11, 2007 |
7269430 |
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10779245 |
May 26, 2009 |
7539501 |
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60544605 |
Feb 13, 2004 |
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60546622 |
Feb 20, 2004 |
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60580026 |
Jun 16, 2004 |
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Current U.S.
Class: |
375/296;
375/295 |
Current CPC
Class: |
H04L
1/0001 (20130101) |
Current International
Class: |
H04L
27/00 (20060101) |
Field of
Search: |
;375/259-260,295
;370/464-466 ;714/752,776,784,786 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Jianhua Liu, Jian Li and Petre Stoica, A MIMO System With Backward
Compatibility for OFDM Based WLANS, 2003 4th IEEE Workshop on
Signal Processing Advances In Wireless Communications,
0/7803-7858-X/03, Jun. 2003, pp. 130-134. cited by other .
XP-002236904, Part 11: Wireless Lan Medium Access Control (MAC) and
Physical Layer (PHY) specifications: High-speed Physical Layer in
the 5 GHZ Band, Sponsor: LAN/MAN Standards Committee of the IEEE
Computer Society, IEEE Std 802.11 a-1999, Sep. 1999, pp. 1-53.
cited by other .
Takeshi Onizawa, Masato Mizoguchi, Masahiro Morikura and Toshiaki
Tanaka, A Fast Synchronization Scheme of OFDM Signals for High-Rate
Wireless LAN, IEICE Trans. Commun., vol. E82-B. No. 2, Feb. 1999,
pp. 455-463. cited by other .
Erik G. Larsson and Jia Li, Preamble Design for Multiple-Antenna
OFDM-Based WLANs With Null Subcarriers, IEEE Signal Processing
Letters, vol. 8, No. 11, Nov. 2001, pp. 285-288. cited by other
.
XP-002298432, 802.11gTM, IEEE Standard for Information Technology.
Part 11: Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) Specifications, Amendment 4: Further Data Rate
Extension in the 2.4 GHz Band, IEEE Computer Society, Jun. 2003,
pp. 1-78. cited by other.
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Primary Examiner: Corrielus; Jean B
Attorney, Agent or Firm: McAndrews, Held & Malloy,
Ltd.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a CONTINUATION OF U.S. application Ser.
No. 11/056,155, filed Feb. 14, 2005, which is a
CONTINUATION-IN-PART of: U.S. application Ser. No. 10/778,754,
filed Feb. 13, 2004, now issued U.S. Pat. No. 7,162,204; U.S.
application Ser. No. 10/778,751, filed Feb. 13, 2004, now issued
U.S. Pat. No. 7,269,430; and U.S. application Ser. No. 10/779,245,
filed Feb. 13, 2004, now issued U.S. Pat. No. 7,539,501.
Said U.S. application Ser. No. 11/056,155 also claims benefit from
and priority to the following U.S. provisional applications: U.S.
Application No. 60/544,605, filed Feb. 13, 2004; U.S. Application
No. 60/546,622 filed Feb. 20, 2004; and U.S. Application No.
60/580,026, filed Jun. 16, 2004.
The above-identified applications are hereby incorporated herein by
reference in their entirety.
Claims
What is claimed is:
1. A wireless communications device, comprising: a transceiver that
transmits and receives radio frequency (RF) signals; and one or
more processors coupled to the transceiver, wherein the one or more
processors are configured to: determine a coding format according
to a signal field; arrange at least one bit in the signal field to
comply with a channel width; and generate a coded signal field
according to the coding format and the at least one bit in said
signal field.
2. The wireless communications device according to claim 1, wherein
the one or more processors are configured to determine a number of
reserve bits in said signal field.
3. The wireless communications device according to claim 2, wherein
the one or more processors are configured to determine that the
number of reserve bits is 6.
4. The wireless communications device according to claim 2, wherein
the one or more processors are configured to determine that the
number of reserve bits is 4.
5. The wireless communications device according to claim 2, wherein
the one or more processors are configured to determine that the
number of reserve bits is 2 or less.
6. The wireless communications device according to claim 1, wherein
the one or more processors are configured to apply a constraint
length to the signal field.
7. The wireless communications device according to claim 1, wherein
the one or more processors are configured to insert at least one
tail bit into the signal field.
8. The wireless communications device according to claim 1, wherein
the one or more processors are configured to code the signal field
using a convolutional code.
9. The wireless communications device according to claim 8, wherein
the convolutional code is used at a 1/2 rate.
10. The wireless communications device according to claim 8,
wherein the convolutional code is used at a 1/3 rate.
11. The wireless communications device according to claim 1,
wherein the one or more processors are further configured to encode
the signal field using a reed-solomon block code.
12. The wireless communications device according to claim 11,
wherein the one or more processors are further configured to
generate at least one codeword during the encoding.
13. The wireless communications device according to claim 1,
wherein the wireless communications device supports 802.11n
communications.
14. The wireless communications device according to claim 1,
wherein the wireless communications device supports cellular
communications.
15. The wireless communications device according to claim 1,
wherein the wireless communications device is a cellular phone.
16. The wireless communications device according to claim 1,
wherein the wireless communications device supports Bluetooth
communications.
17. The wireless communications according to claim 1, wherein the
wireless communications device supports one or more of the
following: global system for mobile communications (GSM), code
division multiple access (CDMA), and wireless local area
network.
18. The wireless communications according to claim 1, wherein the
wireless communications device supports orthogonal frequency
division multiplexing.
19. A wireless communications device, comprising: one or more
transceivers that transmit and receive radio frequency (RF)
signals; and one or more processors coupled to the one or more
transceivers, wherein the one or more processors are configured to:
generate a signal field having a rate/mode sub-field, a length
sub-field, at least one data unit sub-field and a reserved
sub-field; determine a coding format according to the reserved
sub-field; arrange at least one bit in the sub-fields according to
the coding format and a wireless communication standard for the
signal field; and code said signal field with the coding
format.
20. The wireless communications device according to claim 19,
wherein the one or more processors are further configured to
modulate the signal field over a set of subcarriers corresponding
to the wireless communication standard.
21. The wireless communications device according to claim 19,
wherein the one or more processors are configured to generate an
acknowledgement sub-field for the signal field.
22. The wireless communications device according to claim 19,
wherein the one or more processors are configured to generate that
signal field having a length of approximately 26 bits to
approximately 30 bits.
23. The wireless communications device according to claim 19,
wherein the one or more processors are configured to arrange the at
least one bit according to the wireless communication standard and
a legacy communication standard.
24. The wireless communications device according to claim 23,
wherein the wireless communication standard is 802.11n and the
legacy communication standard is one or more of the following:
802.11, 802.11a, 802.11b, and 802.11g.
25. The wireless communications device according to claim 19,
wherein the wireless communications device supports 802.11n
communications.
26. The wireless communications device according to claim 19,
wherein the wireless communications device supports cellular
communications.
27. The wireless communications device according to claim 19,
wherein the wireless communications device is a cellular phone.
28. The wireless communications device according to claim 19,
wherein the wireless communications device supports Bluetooth
communications.
29. The wireless communications according to claim 19, wherein the
wireless communications device supports one or more of the
following: global system for mobile communications (GSM), code
division multiple access (CDMA), and wireless local area
network.
30. The wireless communications according to claim 19, wherein the
wireless communications device supports orthogonal frequency
division multiplexing.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to wireless communication systems
and more particularly to supporting multiple wireless communication
protocols within a wireless local area network by formatting,
modulating, and coding a signal.
2. Description of the Related Art
Wireless and wire lined communications between wireless or wire
lined communication devices use networks and systems to exchange
information and data. Communication systems may include national or
international cellular telephone systems to the Internet to
point-to-point in-home wireless networks. Each type of
communication system may operate in accordance with one or more
communication protocol standards. For example, wireless
communication systems may operate in accordance with one or more
protocol standards including, but not limited to, IEEE 802.11,
Bluetooth, advanced mobile phone services (AMPS), digital AMPS,
global system for mobile communications (GSM), code division
multiple access (CDMA), local multi-point distribution systems
(LMDS), multi-channel-multi-point distribution systems (MMDS), and
the like. The applicable protocol for wireless communications
standard may vary. As the IEEE 802.11 specification has evolved
from IEEE 802.11 to IEEE 802.11b (standard 11b) to IEEE 802.11a
(standard 11a) and to IEEE 802.11 g (standard 11 g), wireless
communication devices that are compliant with standard 11b may
exist in the same wireless local area network (WLAN) as standard
11g compliant wireless communication devices.
When legacy devices such as those compliant with an earlier version
of a standard reside in the same WLAN as devices compliant with
later versions of the standard, mechanisms or processes may be
employed for the legacy devices to know when the newer version
devices are utilizing the wireless channel to avoid interference or
a collision. A legacy system may be an existing system that is in
place and available for use in wireless local area networks. The
issue of legacy systems may be important because these systems may
remain in place after new standards, methods or networks for future
wire local area networks are implemented.
The different protocols or standards may operate within different
frequency ranges, such as 5 to 6 gigahertz (GHz) or, alternatively,
2.4 GHz. For example, standard 11a may operate within the higher
frequency range. An aspect of standard 11a is that portions of the
spectrum, between 5 to 6 GHz, are allocated to a channel for
wireless communications. The channel may be 20 megahertz (MHz) wide
within the frequency band. Standard 11a also may use orthogonal
frequency division multiplexing (OFDM). OFDM may be implemented
over subcarriers that represent lines, or values, within the
frequency domain of the 20 MHz channels. A signal may be
transmitted over different subcarriers within the channel. The
subcarriers may be orthogonal to each other so that information or
data is extracted off each subcarrier about the signal.
Backward compatibility with legacy devices may be enabled at the
physical (PHY) layer or the Media-Specific Access Control (MAC)
layer. At the PHY layer, backward compatibility is achieved by
re-using the PHY preamble from a previous standard. Legacy devices
may decode the preamble portion of all signals, which provides
sufficient information for determining that the wireless channel is
in use for a specific period of time, to avoid interference and
collisions even though the legacy devices cannot fully demodulate
or decode the transmitted frame(s).
At the MAC layer, backward compatibility with legacy devices may be
enabled by forcing devices that are compliant with a newer version
of the standard to transmit special frames using modes or data
rates that are employed by legacy devices. These special frames may
contain information that sets the network allocation vector (NAV)
of legacy devices such that these devices know when the wireless
channel is in use by newer stations.
As new standards or protocols are implemented, backward
compatibility of receiving and transmitting signals may become more
of a concern. New signaling formats may desire more robustness than
legacy formats. Further, frames exchanged within a wireless system
may include immediate acknowledgement capabilities, bursting
information and exchanging more bits of information than frames
used by legacy devices.
SUMMARY OF THE INVENTION
A method for coding a signal for wireless communication is
disclosed. The method includes determining a coding format
according to a signal field. The method also includes arranging at
least one bit in the signal field to comply with a channel width.
The method also includes generating a coded signal field according
to the coding format and the at least one bit in the signal
field.
A method for generating a signal field for wireless communication
also is disclosed. The method also includes coding a signal field
according to a coding format. The coding format uses a
convolutional code having a rate. The method also includes adding a
preamble to the signal field to support communication over a first
channel and a second channel. The first channel is wider than the
second channel. The method also includes modulating the signal
field over a set of subcarriers pertaining to the first
channel.
A method for generating a signal for wireless communication also is
disclosed. The method includes generating a signal field having a
rate/mode sub-field, a length sub-field, at least one data unit
sub-field and a reserved sub-field. The method also includes
determining a coding format according to the reserved sub-field.
The method also includes arranging at least one bit in the
sub-fields according to the coding format and a wireless
communication standard for the signal field. The method also
includes coding the signal field with the coding format.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a wireless communication system in accordance
with the present invention;
FIG. 2 illustrates a wireless communication device in accordance
with the present invention;
FIG. 3 illustrates a diagram of a wide bandwidth channel in
accordance with the present invention;
FIG. 4 illustrates a format of a signal in accordance with the
present invention;
FIG. 5 illustrates a signal field having sub-fields in accordance
with the present invention; and
FIG. 6 illustrates a flowchart for coding and modulating a signal
in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference is now made in detail to the preferred embodiments of the
present invention, examples of which are illustrated by the
accompanying drawings.
FIG. 1 depicts a diagram of a wireless communication system 10
according to the present invention. Communication system 10 may
include stations 14, 16 and 18. Stations 14, 16 and 18 may include
wireless communication devices, such as cellular or wireless
phones, digital devise, laptop or desktop computers, personal
digital assistants, wireless modems, wireless gaming modules, and
the like. Stations 14, 16, and 18 may be coupled to access point
12, which exchanges data or information within communication system
10. Additional stations and applicable devices, or components, may
be coupled to access point 12 within communication system 10.
Communication system 10 may forward data or information in the form
of signals, either analog or digital. Wireless devices or
components within the individual base stations may register with
the base station to receive services or communications within
communication system 10. Wireless devices may exchange data or
information via an allocated channel within access point 12. Access
point 12 may establish local area networks (LANs), wide area
networks (WANs), wireless local area networks (WLAN), ad-hoc
networks, and the like.
Communication system 10 may operate under various protocols or
standards to support wireless communication. For example,
communication system 10 may operate under the IEEE 802.11n
(standard 11n) standard for wireless communications. Standard 11n
may be considered a current standard or protocol, while the other
standards, such as standard 11a, may be considered legacy
standards. Alternatively, communication system 10 may operate under
a variety of standards, such as standard 11a, standard 11g, and
standard 11n. Communication system 10 also may include legacy
devices or components that do not support current standards. For
example, certain legacy devices or components may comply with
standard 11a, while newer devices or components may comply with
standard 11n.
Standard 11n may occupy the 5-6 GHz band, or, alternatively,
standard 11 may occupy the 2.4 GHz band. Standard 11n may be
considered an extension of standard 11a, with improvements.
Standard 11n devices and components may operate throughput of 100
Mbps or more, at the MAC. The physical layer rate for standard 11n
devices and components may be greater than those of legacy
protocols or standards. Further, the bandwidth for channels under
standard 11n may be 20 MHz, or 40 MHz. Thus, standard 11n may
implement wider channels than previous standards.
Wireless communications using standard 11n may occur on different
mediums or using different configurations. For example, multiple
antennas may be used in communication system 10 via station 16. The
multiple antennas may act as multiple transmitters and multiple
receivers so that several signals may be exchanged. The number of
transmitters or receivers may depend on the number of data streams.
Thus, communication 10 may include, as discussed above, multiple
input, a multiple output (MIMO) structure. MIMO structures, or
configurations, may improve robustness of wireless communications
in a communication system 10. To better improve robustness,
communication system 10 may have the number of data streams to be
less than the number of transmitters.
Communication system 10, under standard 11n, may desire high
throughput wireless communication between, for example, a device in
station 14 to a device in station 16. Access point 12, along with
stations 14, 16 and 18 may form mixed networks, such as WANs, LANs,
and the like, from standard 11a and standard 11n devices. These
networks may include "Greenfield" heterogeneous networks of
standard 11n devices that occupy 20 MHz and 40 MHz channels. A
presumption may exist that stations 15, 16 and 18 can receive all
signals, no matter which standard is in effect.
FIG. 2 is a block diagram illustrating a wireless communication
device 200 according to the present invention. Wireless device 200
may include host device 18 and an associated radio, or station, 60.
For cellular telephone hosts, radio 60 may be a built-in component.
For personal digital assistants hosts, laptop hosts, or personal
computer hosts, radio 60 may be built-in or an externally coupled
component. Radio 60 also may be compliant with one of a plurality
of wireless local area network (WLAN) protocols including, but not
limited to, standard 11n.
Host device 18 may include processing module 50, memory 52, radio
interface 54, input interface 58 and output interface 56.
Processing module 50 and memory 52 execute the corresponding
instructions that may be executed by host device 18. For example,
for a cellular telephone host device, processing module 50 may
perform the corresponding communication functions in accordance
with a particular cellular telephone standard.
Radio interface 54 allows data to be received from and sent to
radio 60. For data received from radio 60, or inbound data, radio
interface 54 may provide the data to processing module 50 for
further processing or routing to output interface 56. Output
interface 56 provides connectivity to an output display device such
as a display, monitor, speakers and the like, such that the
received data may be displayed. Radio interface 54 also provides
data from processing module 50 to radio 60. Processing module 50
may receive the outbound data from an input device such as a
keyboard, keypad, microphone and the like, via input interface 58
or generate the data itself. For data received via input interface
58, processing module 50 may perform a corresponding host function
on the data or route it to radio 60 via radio interface 54.
Radio, or station, 60 may include a host interface 62, a baseband
processing module 64, a memory 66, a plurality of radio frequency
(RF) transmitters 68-72, a transmit/receive (T/R) module 74, a
plurality of antennas 82-86, a plurality of RF receivers 76-80, and
a local oscillation module 100. Baseband processing module 64, in
combination with operational instructions stored in memory 66, may
execute digital receiver functions and digital transmitter
functions, respectively.
Baseband processing modules 64 may be implemented using one or more
processing devices. Such a processing device may be a
microprocessor, micro-controller, digital signal processor,
microcomputer, central processing unit and the like. Memory 66 may
be a single memory device or a plurality of memory devices. When
processing module 64 implements one or more of its functions via a
state machine, analog circuitry, digital circuitry, or logic
circuitry, the memory storing the corresponding operational
instructions is embedded with the circuitry comprising the state
machine, analog circuitry, digital circuitry, or logic
circuitry.
In operation, radio 60 may receive outbound data 88 from host
device 18 via host interface 62. Baseband processing module 64
receives outbound data 88 and, based on a mode selection signal
102, produces one or more outbound symbol streams 90. Mode
selection signal 102 may indicate a particular mode. For example,
mode selection signal 102 may indicate a frequency band of about
2.4 GHz, a channel bandwidth of 20 or 22 MHz, and a maximum bit
rate of about 54 megabits-per-second. Mode selection signal 104 may
indicate a particular rate ranging from 1 megabit-per-second to 54
megabits-per-second. In addition, mode selection signal 102 may
indicate a particular type of modulation, which includes, but is
not limited to, Barker Code Modulation, BPSK, QPSK, CCK, 16 QAM or
64 QAM.
Baseband processing module 64, based on mode selection signal 102
produces one or more outbound symbol streams 90 from output data
88. For example, if a mode selection signal 102 indicates that a
single transmit antenna is being utilized for a particular mode
that has been selected, baseband processing module 64 may produce a
single outbound symbol stream 90 for wireless device 200.
Alternatively, if mode select signal 102 indicates 2, 3 or 4
(multiple) antennas, baseband processing module 64 may produce 2, 3
or 4 (multiple) outbound symbol streams 90 corresponding to the
number of antennas of wireless device 200.
Depending on the number of outbound streams 90 produced by baseband
module 64, a corresponding number of the RF transmitters 68-72 may
be enabled to convert outbound symbol streams 90 into outbound RF
signals 92. Transmit/receive (T/R) module 74 may receive outbound
RF signals 92 and may provide each outbound RF signal to a
corresponding antenna 82-86.
When radio 60 is in a receive mode, T/R module may 74 receive
inbound RF signals 94 via antennas 82-86. T/R module 74 provide
inbound RF signals 94 to RF receivers 76-80. RF receivers 76-80 may
convert inbound RF signals 94 into a corresponding number of
inbound symbol streams 96. The number of inbound symbol streams 96
may correspond to the particular mode in which the data was
received. Baseband processing module 60 receives inbound symbol
streams 90 and converts them into inbound data 98, which is
provided to host device 18 via host interface 62.
Thus, wireless device 200 may generate and exchange signals within
a wireless communication system 10, as shown in FIG. 1. Some
features and functions of wireless device 200 may be found in
current and legacy devices in a wireless communication system.
Wireless device 200 also may react differently to signals supported
by different standards or protocols.
In communication system 10 of FIG. 1, the communication device may
be a newer device as described with reference to FIG. 2, or may be
a legacy device, compliant with an earlier version or predecessor
of standard 11n. The newer devices may configure the channel
bandwidth in a variety of ways.
FIG. 3 depicts a diagram of a wide bandwidth channel 310 including
channels 300 and 302 according to the present invention.
Wide bandwidth channel 310 may be a 40 MHz channel capable of
supporting signals according to MIMO protocols, such as standard
11n. Channels 300 and 302 may be smaller than wide bandwidth
channel 310. For example, channels 300 and 302 may be 20 MHz
channels and compatible with legacy standards, such as standard
11a, that may not support MIMO communications.
Guard band 312 also may be included in a wide bandwidth channel
310. During activation of wide bandwidth channel 310, guard band
312 may be filled with signal data or information. When channels
300 and 302 are activated, guard band 312 may not be filled. Thus,
guard band 312 may be a gap between two legacy channels, such as
channels 300 and 302. Further, wide bandwidth channel 319 includes
a wider band than two legacy channels put together. Devices and
components may desire to know whether a signal is formatted under
standard 11n to use a wide bandwidth channel 310 or, for example,
standard 11a to use channels 300 and 302. Failure to properly do so
may result in interference or collision of signals. For example, if
a signal formatted under standard 11n is placed in channels 300 and
302, then information or data may be lost because guard band 312 is
not accounted for.
To construct wide bandwidth signal 310 without regard as to whether
legacy devices are present, the overlapping legacy portions of
channels 300 and 302 are considered when establishing the format
for wide bandwidth channel 310. The preamble of wide bandwidth
signal 310 may include a legacy header portion or a preamble in
accordance with an earlier version or predecessor of standard 11n
within the header spectral portion of channel 300, or channel 302.
Legacy devices may be able to recognize the frame within wide
bandwidth signal 310 and, based on the information contained within
the preamble, refrain from transmission until wide bandwidth signal
310 has been transmitted.
For communication devices capable of receiving a wide bandwidth
signal, the frames of the signals may include data or header
information within guard band 312 of legacy channels, as discussed
above. This feature may expand the amount of data that may be
transmitted within a frame.
The preamble and packet header of a wide bandwidth signal using
wide bandwidth channel 310 may use the same spectrum that the
payload of a wide bandwidth signal uses to provide a legitimate
preamble and packet headers that can be transmitted in the portion
of the spectrum used by legacy devices. Further, energy of the
signal may be transmitted in the legacy guard bands so that a
receiver may perform reliable preamble processing, such as carrier
detection, gain control, channel estimation and the like, on the
wide-bandwidth signal.
The multiple-channel legacy preambles and packet headers may allow
legacy station reception of the preamble and reliable carrier
detection, gain control, and channel estimation over the legacy
channels. The guard-band transmission may allow for reliable
carrier detection, gain control, and channel estimation for the
remainder of the spectrum that may be used for transmission of the
wide bandwidth payload. Further, legacy stations may be tolerant of
adjacent channel transmissions that are at the same power as the
desired signal. Further, legacy stations may identify legitimate
preambles and packet headers so that the stations are able to
detect that a signal is present, perform gain control, channel
estimation, and other preamble processing, or decode the packet
header to defer transmission until the end of the wide-band
transmission. Energy transmitted in guard band 312 may be
disregarded by the receiver and may not hinder the reception of the
legacy components of a wide-band signal.
For the newer devices that are standard 11n compliant, the devices
may provide more energy for carrier detection, may perform a better
estimate of received power, may do better to gain control on a
packet, may estimate the channel response in a guard band 312 for
use during payload demodulation, and may have full access to the
medium because legacy stations see the transmission and defer until
its end.
For example, channel 300 may operate within the region of 5230 and
5250 MHz. As shown in FIG. 3, the edges of the 20 MHz channel may
taper off. Thus, a gap may arise at the edges of the channel.
Referring to channel 302, it may operate within the region of 5750
and 5270 MHz, and have gaps similar to channel 300. Standard 11n
networks may fill these gaps in order to increase the number of
bits transmitted per time period. Thus, standard 11n-based devices
and networks may process more than twice as much information or
data as a single channel-based system.
Long training for a wide bandwidth signal with wide bandwidth
channel 310 may correspond to long training associated with
standard 11a. Standard 11n may use long training in the preamble of
a frame or packet for channel timing sequence, channel sounding,
channel estimation and the probability of reception. The preamble
portion of a packet for standard 11n may be important for
implementing the applicable standard and making sure the proper
transmission or reception of the signals within a system is
performed. Further, the preamble may have legacy compatibility such
that the packet does not have interface errors or problems with
legacy systems as discussed above. The preamble to a signal or the
signal itself should be useful for new stations according to the
new standards, but not incompatible with old stations.
Standard 11n may allow wireless communications to be more robust
because of increased rates, modes, number of antennas, and the
like. For example, standard 11n may use 6 bits to convey rate
information and other data. The information may include the number
of antennas and modes. A receiver, however, may need to know when
it has received in the last frame and other data bursts according
to standard 11n. All frames also may have immediate acknowledgement
of frame reception in standard 11n. Acknowledgements may occur at
the end of a frame. Because a signal in standard 11n may transmit
more bits of information to increase performance, there may be more
combinations of the numbers of antennas. This aspect may be
important because of the MIMO structure supported by standard 11n.
Standard 11n may be more robust than legacy systems, such as those
implemented under standard 11a. Extra modes may exist, while the
length of a frame, or its preamble, may be the same. As in standard
11a, standard 11n may use 6 bits but allow 64 modes. These modes
may include modulation, encoding, encoding rate, types of encoding
and the number of antennas. Bits may convey this information broken
up into any proportion of the bits added to the signal.
FIG. 4 depicts a format of a backward compatible signal 400 and its
fields according to the present invention. Signal 400 also may be
referred to as a frame. Signal 400 may be supportable by current
and legacy devices within a wireless communication system, such as
communication system 10 shown in FIG. 1. Signal 400 may be
generated for transmission within a wireless device or component,
such as wireless device 200 shown in FIG. 2. With regard to legacy
devices, signal 400 may convey information or data on payload
rate/mode, payload length in bytes, and error check capability.
With regard to current, or MIMO devices, signal 400 may convey
information or data on PNY-related MAC enhancements, such as data
unit bursting, and a more robust error check capability. A more
robust error check capability may reduce the likelihood of false
signal field acceptance as legacy error check capability may be
weak.
Signal 400 may include a legacy preamble 402, a signal field 404,
an extended preamble 406, a plurality of additional signal fields
400, a plurality of data units (Service/PSDU) 410, and an
interframe gap 412. Signal field 414 and PSDU 410 may be the last
fields within signal 400 of their respective pluralities. Initial
signal field 404 may inform the legacy devices of the duration of
the frame so that the legacy devices do not attempt to access a
channel while in use by newer devices. Signal field 404 also may
inform the devices of the channel usage for standard 11n
transmission and the number of applicable transmit antennas.
Additional signal fields 408 and 414 of signal 400 may allow the
signal format to be more robust. A signal for use according to
standard 11n may be more robust than signals in legacy systems.
Thus, additional signal fields 408 and 414 may correlate to the
rate, mode, number of antennas and a checksum. Signal 400 may use
about 6 bits to convey the information or data. The number of bits
used by signal 400, however, may vary as desired, such as 5 bits or
7 bits.
Signal 400 also may be subject to bursting. During a burst, the MAC
may send frames in signal 400 without interframe spacing, so that
the frames are placed together. The burst length may be conveyed at
the end of the burst, with a bit being denoted as a "Last PDSU."
Alternatively, another applicable identifier may be used to
acknowledge the last frame.
Signal 400 may be implemented for high throughput communications,
such as a standard 11n network or system, or a mixed network of
legacy and standard 11n devices. These networks may include
"Greenfield" networks having standard 11n devices that occupy 20
MHz and 40 MHz channels. Signal 400 may be compatible with both
channels, as discussed above. Signal 400 also may be compatible
with "Brownfield" networks having current and legacy devices.
FIG. 5 depicts a signal field 500 having sub-fields according to
the present invention. Signal field 500 may be incorporated into a
signal or frame for transmission in a wireless network or system.
Signal field 500 may be used in legacy devices or components, or in
mixed networks having current and legacy devices or components.
Signal field 500 may inform legacy devices or components of the use
of standard 11n signals to limit medium contention between 20 MHz
and 40 MHz channels. Signal field 500 also may inform standard 11n
devices or components of the number of transmit antennas employed
to indicate whether additional training sequences may follow for
standard 11n usage. Signal field 500 also may provide information
or data on rate/mode, length, the last PSDU in a burst, immediate
acknowledgement requirement and an error check capability.
Thus, signal field 500 may indicate rate/mode sub-field 502, length
of the frame sub-field 504, last PSDU in the frame sub-field 506,
and a PSDU immediate acknowledgement (ACK) sub-field 508. Rate/mode
sub-field 502 may be about 6 bits in length to convey the number of
transmit antennas. A legacy signal field may be absent in a
homogeneous standard 11n case. Rate/mode sub-field 502 also may
convey channel width, such that standard 11n signal field
transmitted by either 20 MHz or 40 MHz channel devices should be
receivable by either 20 M Hz or 40 MHz channel devices. PHY data
rates may span 6 mbps through 448 mbps, with roughly 33% throughput
increase with each higher data rate. Sixteen rates may be required,
or 4 bits, in rule/mode sub-field 502 to allow 4 modes for
achieving any given rate by varying channel width, subcarrier
constellation size, number of transmit antennas and the like, or 2
bits of information or data.
Length portion sub-field 504 of signal field 500 may be about 12
bits to allow PSDUs up to 4095 bytes long as allowed in a legacy
case. MAC level extension for PSDU bursting may not be represented
in length as a Burst ID or Burst Length because burst length may be
unknown at start of burst or, even if burst length is known, may be
conveyed once at start or end of burst. Thus, no need may arise to
index PSDUs in a burst at the PHY level because MAC methods may
exist for unique PSDU identification.
Last PSDU sub-field 506 of signal field 500 may be about 1 bit to
convey burst length at the end of a burst, with the bit denoting
"Last PSDU." Immediate ACK sub-field 508 of signal field 500 may be
about 1 bit to resolve contention between responding devices when a
series of Immediate MAC acknowledgements are required to the series
of PSDUs in a transmitted burst.
Signal field 500 also may include reserved sub-field 510 and CRC
sub-field 512. Reserved sub-field 510 may be about 2-6 bits long
depending on a chosen coding option. Reserved bits within reserved
sub-field 510 may be reallocated to other fields within signal
field 500, such as rate/mode field 502 or length field 500, such as
rate/mode field 502 or length field 504, as necessary. CRC
sub-field 512 may be about 4 bits and may provide error detection
that is improved over a single parity bit in a legacy signal field.
These bits also may be referred to as the checksum for signal field
500.
Immediate ACK sub-field 508 may provide immediate acknowledgement
regarding signal field 500. Immediate acknowledgement of signal
field 500 may be appropriate when bursting occurs so that frames
are sent from the MAC without interframe spacing. The MAC may
require that the frames have an acknowledgement policy, and frames
may incorporate different policies. The acknowledgement may serve
to let transceivers know when it is receiving the last frame in the
burst. The acknowledgement is known as "immediate" because the MAC
receives acknowledgement from the frame having signal field 500
without waiting for acknowledgements from other frames. Thus, once
frames are received, they are acknowledged as soon as possible.
Immediate ACK sub-field 508 may be about 1 bit long.
Thus, signal field 500 may have a length of about 26-30 information
bits, but may remain at least as robust in performance and offer
superior error detection capacity when compared to legacy standards
or protocols. Performance may indicate the signal-to-noise ratio
(SNR) desired to achieve a given probability of signal field error.
Moreover, signal field 500 and the applicable sub-fields may be
subject to coding and modulation with the signal, but may not lose
or reduce its robustness.
FIG. 6 depicts a flowchart for coding and modulating a signal field
according to the present invention. Proper coding and modulating
the signal field may be determined by the applicable standard or
protocol. A signal field used under standard 11n may allow 26-30
information bits, as discussed above. Legacy coding and modulation
may allow 24 uncoded bits per signal field, with 18 information
bits available and the remaining 6 bits acting as tail bit for
immediate decoding. Thus, coding and modulation of the signal
fields may account for these differences.
Step 602 executes by receiving a signal field that is to be
transmitted in a frame of a signal in a wireless communication
system. The signal field may be a specified length of about 26-30
bits. Alternatively, the received signal field may be of a
different length, as appropriate. Step 604 executes by determining
the number of reserved information bits in the signal field. Coding
of the received signal field may occur according to three different
options. The applicable option may depend upon the number of bits
that are reserved in the signal field.
Step 606 executes by determining whether six reserved information
bits are in the signal field. If yes, step 608 executes by applying
a legacy constraint length. The legacy constraint length may be
about 6 bits. Step 610 executes by executing a 1/2 convolutional
code over the signal. For example, for signal field length of 96
coded bits, step 610 may convolutionally code 48 bits. A coded
signal configuration may be desirable because it can out-perform an
uncoded signal configuration. The code also may return to a known
state in order to be effectively executed. Step 612 executes by
inserting bits in the transmitted sequence. For example, 18 tail
bits may be inserted in to the signal field. These 18 tail bits may
include 12 tail bits in addition to 6 legacy tail bits. Step 614
executes by arranging the uncoded bits and tail bits. For example,
the bits may be arranged as follows: 10 information, 6 tail, 10
information, 6 tail, 10 information and 6 tail. The sum of the
arranged bits may be 30 information bits that is added to 18 tail
bits to generate 48 uncoded bits, or, subsequently, 96 coded bits
per signal field.
If step 606 determines that there is not 6 reserved information
bits, then step 616 executes by determining whether 4 reserved
information bits are in the signal field. If yes, step 618 is
executed by applying an outer Reed-Solomon block code. The outer
Reed-Solomon block code may be known as a (7,5) RS block code. Step
618 may include using two code words when applying the outer
Reed-Solomon code. The code words may be about 21 bits in length.
The code words are generated by grouping 15 information bits into 5
elements, and 6 parity bits into 2 elements. The parity bits may be
added by Reed-Solomon encoding. The encoding results in 21 block
coded bits, or 1 Reed-Solomon code word. Two Reed-Solomon code
words may be used to get 42 bits. Step 620 executes by applying the
legacy constraint length. The legacy constraint length may be about
6 tail bits. This constraint may result in 48 bits when the tail
bits and the 2 Reed-Solomon code words are added together. Step 622
executes by executing the 1/2 convolutional code to the tail bits
in the code words. The result may be 96 coded bits. Further, 6 tail
bits may be appended to the coded bits so that 12 parity bits may
exist with 6 bit errors that can be corrected. Thus, 30 information
bits may exist along with 18 tail bits.
If step 616 is no, then step 624 is executed by applying the legacy
constraint length to the signal field. The legacy constraint length
may be about 6 bits. Step 626 executes by executing a 1/3
convolutional code over the signal field. Thus, step 626 may encode
over the whole signal field. Step 628 executes by appending bits
within the signal field. Six tail bits may be appended. A resulting
signal field may be 26 information bits and 6 tail bits to equal 32
uncoded bits, or 96 coded bits for signal field.
Step 640 may execute by applying quadrature phase shift key
modulation in 48 data bearing sub-carriers that allows 96 coded
bits for a signal field. The 96 coded bits that result from the
above 3 options may be modulated with QPSK over 48 tones. These
tones may correspond to the sub-carriers. Sub-carriers supported by
standard 11n are activated according to this modulation. For 40 MHz
channel usage, 48 sub-carriers may be replicated in upper and lower
20 MHz halves to allow standard 11n signal field demodulation by
legacy, or 20 MHz, channel devices. Step 650 executes by generating
the appropriate header for the signal field such that the signal
field may be transmitted and received within a wireless
communication system with an increased probability of correct
reception and in a more robust manner.
As discussed above, three options may be used in coding a signal
field. The above options are distinguished according to the number
of reserved bits. The options also may be distinguished or applied
according to different criteria and their application is not
dependent upon the number of reserved bits. For example, one option
may be chosen to code all signal fields received in a device or
component according to the present invention. Alternatively, two
out of the three options may be employed and distinguished from
each other according to different criteria, such as memory
constraints or complexity of the convolutional code.
Packets having the signal field as discussed above may include
headers greater than an 18 bit header found in legacy packets.
Despite being larger, a generated header may be as robust as
possible while transmitting more information bits than legacy
signal fields.
The preceding discussion has presented various embodiments for
wireless communications in a network that includes legacy devices.
As one of average skill in the art will appreciate, other
embodiments may be derived from the teachings of the present
invention without deviating from the scope of the claims.
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